1. Field of the Invention
The present invention relates to an aqueous chemical treating composition for use with glass fibers. More specifically, the invention relates to an aqueous chemical treating composition having a simplified composition with increased stability and reduced settling characteristics which is useful in reinforcing polymers. The aqueous chemical treating composition further utilizes a simplified epoxy emulsion or dispersion.
2. Description of the Prior Art
Glass fibers, in various forms, are utilized in a variety of durable lightweight materials. The glass fibers may be provided in several forms, which are then incorporated into a polymeric matrix such that they can be shaped and fixed in particular hardened forms. The glass fiber itself is utilized in a variety of forms. Each of these forms begins with the basic glass fiber, which is formed in a process which draws molten streams of glass material from a flowing reservoir of molten glass. The glass material has a composition such that the glass may be drawn into thin resilient fibers having mechanical characteristics which permit flexure and manipulation of the fiber after drying. The molten stream of fiberizable glass material is passed over a bushing which provides a plurality of holes through which the glass material may be drawn. The molten material is passed through the bushing, forming a plurality of glass fibers. Immediately after the newly formed glass fibers are drawn from the bushing, a chemical treating composition is applied to their surfaces. This chemical treating composition, or sizing, is usually an aqueous composition and is formed of a variety of components. The sizing is primarily utilized to retard abrasion between the glass fibers when they are gathered onto a variety of storage media such as a spool. The sized glass fiber strand additionally has improved strength and flowability when compared to the non-sized fiber strand.
The glass fibers which have been sized are collected into a forming package, which is a winding of continuous strand or strands. Alternatively, the strands are chopped during their formation in a process known as wet chopping. Either of these two processes can terminate in a drying step to remove moisture from the strands. The dried continuous strands of multiple forming packages may be combined to form a roving, which may be chopped in its dried form. A single strand of a single forming package may also be chopped. Either process involving the chopping of a dried strand is known as dry chopping.
Once the sized glass fiber has been chopped, it can be introduced into a thermosetting or thermoplastic polymeric substrate and can be utilized to reinforce that substrate and provide improved strength while retaining a relatively light weight. The manipulation of the chopped, sized glass fiber during introduction of that fiber into the polymeric composite requires good flowability of the chopped strands. This good flowability is achieved by reduction of interstrand friction and is provided by the dried sizing on the surface of the strands. Furthermore, during chopping, the glass fibers may fray or splinter at the chopped ends. This produces a large number of small abrasive particles which may abrade or damage the otherwise acceptable fibers. The sizing is utilized to protect the glass fibers from abrasion during formation and processing and further increases the integration of the strand to reduce the breakdown of the strand into filaments or slivers when chopped. This increased strand integrity must further be retained after chopping to provide added strength when the fiber is incorporated in the polymeric material.
Fiber reinforced composites can be produced from thermosetting molding compounds such as bulk molding compound and sheet molding compound or from thermoplastic molding compounds. The bulk molding compound is generally a resin-based compound having short glass fibers impregnated therein. These short glass fibers are generally of a length of about 1/8 to 1/2 inch. The other components of the bulk molding compound include fillers, pigment, a catalyst, thickeners and other specialized additives which vary based on the application of the ultimately formed compound. The bulk molding compound typically has a glass content between 10 and 25 weight percent and is generally formed into logs or ropes. The sheet molding compound is also a resin-based compound further incorporating filler, chopped strand reinforcement, a release agent and a catalyst which is processed into a sheet form. The sheet molding compound may also include chemical thickeners such as alkaline earth oxides and hydroxides to increase the viscosity of the material. As opposed to the bulk molding compound, the glass fiber is chopped to a length of 1/2 to 1 inch for this application and is utilized in a weight range of approximately 25 to 45 percent. The sizing composition also protects the glass fibers from abrasion during the formation of the compounds and further increases the compatibility between the glass fibers and the substrate within which they are to be dispersed. The sizing compound reduces abrasion both between glass fibers themselves and between glass fibers and the polymeric matrix.
Glass fiber is also utilized to reinforce polymeric matrixes for use in clear or translucent reinforced plastic panels. These panels are utilized in solar collectors, skylights, light fixture covers and the like, and require glass fibers having particular optical characteristics in addition to the strength and mechanical characteristics previously described. The glass fibers must not reduce the clarity of these panels and must be even more completely and consistently dispersed throughout the matrix to provide consistent optical characteristics. In the optical environment, it is desirable to achieve a fast wet-out of the glass fibers in the polymeric matrix. Wet-out is a characteristic which refers to the encapsulation of the glass fibers by the matrix polymer. This is a measure of the apparent intimacy of contact between the polymeric matrix and the glass fibers. The polymeric matrix should quickly and easily envelop the glass fibers to provide a smooth and uniform compound without external visibility of the glass fibers within the material. The processability, curing characteristics and surface properties of the final material will be affected if fast wet-out is not achieved.
A number of sizing compositions for glass fibers have been developed to address these particular needs and to achieve these characteristics with the minimum number of components and mixing steps. Typically sizing compositions are aqueous compositions utilizing lubricants, film formers, coupling agents, wetting agents and emulsifiers to provide these characteristics. Temple, U.S. Pat. No. 4,394,418, issued Jul. 19, 1983, discloses an aqueous sizing composition utilizing aqueous, dispersible, emulsifiable or solubiltzable film formers including a vinyl acetate-organo silane copolymer and a 1,2-polyepoxide polymer having a weight ratio of 95 to 5 to 5 to 95 weight percent between the silane copolymer to the polyepoxide polymer. The disclosed aqueous sizing composition also utilizes one or more non-ionic surfactants in an aqueous, dispersible, solubilizable or emulsifiable polyamide and/or fatty acid amide and at least one silane coupling agent which is an epoxy-containing organo silane coupling agent or an amino-containing organo silane coupling agent or a mixture thereof. The aqueous sizing composition also has a blend of an aqueous, dispersible, solubilizable or emulsifiable polyethylene containing polymer and a wax where the weight ratio of the polyethylene-containing polymer to wax is in the range of about 25 to 1 to about 1 to 25. In certain circumstances the wax may be deleted or reduced. Water is also present and the sizing composition may contain an organic hydrocarbon acid or polyacid to provide a pH of between 4 and 9.
The nonionic surfactants disclosed in the Temple reference are specifically described as having a hydrophilic/lipophilic balance (HLB) in the range of about 10 to 20 and alkyl aryl polyether nonionic surfactant is preferably utilized having an HLB of 14. The nonionic surfactant is provided in the weight percent range of between 0.05 to 3 of the entire composition and approximately 0.1 to 5 weight percent of the total solids.
The use of surfactants is also disclosed in Sanzero, U.S. Pat. No. 4,752,527, issued Jun. 21, 1988. The Sanzero reference discusses the use of condensates of ethylene oxide with hydrophobic bases formed by condensation with propylene oxide and propylene glycol. The reference utilizes these surfactants in a sizing composition formed by a polyester resin combined with an epoxy resin a polyethylene glycol emulsifier, octylphenoxypolyethylene oxyethanol emulsifier, polyvinyl pyrrolidone film former, methacryloxypropyltrimethoxysilane, acetic acid and a glass fiber lubricant. The references teaches only the use of the methacryloxypropyltrimethoxysilane coupling agent. Furthermore, a strand hardening agent is preferred to overcome a detrimental quantity of chopper cling.
It has been recently discovered that the previously discussed emulsion surfactants can have limited stability characteristics. It is generally observed that micelles agglomerate and settle out within one-half to two hours. This requires a vigorous agitation shortly before any use of the mixture which may be very inconvenient in a commercial setting.
There remains, therefore, a need in the art for a simplified sizing composition which provides improved strength and flow properties when applied to glass fibers which are utilized in a thermosetting polymeric composite and which exhibits extended stability times. This will reduce the amount of handling attention required when utilizing the compound in a commercial setting. Additionally, there remains a need in the art for the use of a simpler sizing composition which exhibits improved stability. This sizing compound should further provide increased wet-out and mechanical properties imparted to the glass fiber to reduce filamentization and particle creation during the chopping process.